1. Field of the Invention
The present invention relates to a laminated coil array including a plurality of coil conductors embedded in a ceramic laminate.
2. Description of the Related Art
Among laminated coil arrays used for noise elimination in OA equipment, such as computers, there is a laminated coil array described in Japanese Unexamined Patent Application Publication No. 2001-23822. As shown in FIG. 6, this laminated coil array 91 includes ceramic layers 33, on the surface of which internal conductors 34 to 37 are provided. The internal conductors 34 are electrically connected in series through via holes 43 provided in the ceramic sheets 33 to define a spiral coil conductor L1. In the same manner, the internal conductors 35, 36, and 37 are also electrically connected in series through via holes 43 to define spiral coil conductors L2, L3, and L4.
As shown in FIG. 6, the ceramic layers 33 are laminated in order and, after the ceramic layers 32 including via holes 42 are disposed on their top and bottom surfaces, the layers are integrally fired to form a laminate 45 as shown in FIG. 7. External electrodes 51 to 54 are disposed on the end surfaces of the laminate 45. The external electrodes 51 to 54 are electrically connected to the end portions of the coil conductors L1 to L4 which are led out to the surface of the laminate 45 through via holes 42.
In the laminated coil array 91 having the structure described above, when the coil conductors L1 to L4 are arranged close together in the laminate 45 to reduce the size of the laminated coil array 91, the inductances of the coil conductors L1 to L4 have different values.
That is, in the coil conductors L1 and L4 located at both end portions in the arrangement direction of the coil conductors L1 to L4 in the laminate 45, the magnetic path is narrowed at the end portions of the laminate 45. Therefore, the inductance of the coil conductors L1 and L4 is less than that of the coil conductors L2 and L3 not located at both ends in the arrangement direction of the coil conductors L1 to L4.